1. Field
The present application generally relates to optical metrology, and, more particularly, to allocating processing units in a computer system to generate simulated diffraction signals used in optical metrology.
2. Related Art
In semiconductor manufacturing, periodic gratings are typically used for quality assurance. For example, one typical use of periodic gratings includes fabricating a periodic grating in proximity to the operating structure of a semiconductor chip. The periodic grating is then illuminated with an electromagnetic radiation. The electromagnetic radiation that deflects off of the periodic grating are collected as a diffraction signal. The diffraction signal is then analyzed to determine whether the periodic grating, and by extension whether the operating structure of the semiconductor chip, has been fabricated according to specifications.
In one conventional optical metrology system, the diffraction signal collected from illuminating the periodic grating (the measured-diffraction signal) is compared to one or more simulated-diffraction signals. Each simulated-diffraction signal is associated with a hypothetical profile. When a match is made between the measured-diffraction signal and one of the simulated-diffraction signals, the hypothetical profile associated with the simulated-diffraction signal is presumed to represent the actual profile of the periodic grating.
The simulated-diffraction signals used in optical metrology can be generated using a numerical analysis technique, such as rigorous coupled wave analysis (RCWA). More particularly, in the diffraction modeling technique, a simulated diffraction signal is calculated based, in part, on solving Maxwell's equations. Alternatively, the simulated diffraction signals can be generated using a machine learning system (MLS). Generating the simulated diffraction signal, however, involves performing a large number of complex calculations, which can be time consuming and costly.